I’ve used: User Agent Switcher

Successfully using;

1. Whitelist mode
2. Domain = teams.microsoft.com
3. UserAgentString = Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36

They support meetings in Firefox so it’s a bit weird why they would block calls… They’re effectively the same thing

Additionally, if you change your userAgent to be Chrome things are working pretty good in Firefox as far as I’ve tried it (not too extensively)